Is there a way to place a material over other materials (subdermal base)
Try using the Principled shader. It has SSS, diffuse, and roughness all built in. Connect the subdermal texture to the SSS color input, the skin texture to the color input, and set the SSS amount to something other than 0. You will probably have to adjust the subsurface radius to get it looking right. If I recall correctly, you want the red value (the top one) to be the highest by a fair bit, then green, with blue slightly below green. The radius is essentially the 'depth' of the scattering effect for each light color (RGB). Human skin is red when you shine a light through it, so that is why you will want the red value to be higher. I believe the radius is in blender units, so keep that in mind with the scale of your object. You don't want the radius to be larger than the width of your model, as that will make the entire hand translucent, and look fake.

Some other things to consider to get great looking skin is some subtle bump and a roughness texture (using the Principled roughness and normal). That will really help make the skin look realistic, as skin has some subtle reflections and surface texture.